1. Field of the Invention
The present invention relates generally to the treatment of tumors, in particular the treatment of tumors using an interferon. More specifically, the invention relates to the use of dipyridamole for enhancing the tumor-growth inhibitory action of an interferon, a method of treating a patient suffering from a tumor by combined therapy with dipyridamole and an interferon, the use of dipyridamole and interferon for preparing such pharmaceutical preparations for treating tumors, and to pharmaceutical preparations so produced.
2. Brief Description of the Backoround Art
Information on the inhibitory action of human interferon (HuIFN) on the growth of cultured cell lines has been accepted as viable for clinical trials of HuIFN as antitumor therapy (Adv. Cancer Res., Vol. 46, Academic Press. London (1986), and Stewart, The Interferon System. Springer-Verlag, Wien/New York, (1981).
Recently, it has been found that the susceptibility of human cells to the anticellular effects of HuIFN correlated with radio-sensitivity and/or DNA-repair capacity. Suzuki et al., Virology. 135:2029, (1984); Mutation Res., 106:357-376, (1982); J. Gen. Virol., 67.651-661 (1986), Yarosh et al., Carcinooenesis. 6:883-886 (1985) Biophys. Res. Commun., 72:732 (1976). It has also been found that the cellular response mechanisms for DNA damage are modified by HuIFN treatment itself; for example, the increase of DNA-repair synthesis levels and enhancement of survival of cells treatment with agents which can cause structural damage of DNA. Suzuki et al., Virology, 135:20-29, (1984); Mutation Res., 175: 189-193 (1986). Therefore, it seems undesirable to carry out antitumor therapy by HuIFN in combination with other anti-cancer agents which damage DNA because of HuIFNinduced resistance to the agents, and there is a need for an agent which does not itself cause DNA damage but can enhance the antitumor activity of interferon.
The compound 2,6-bis(diethanolamine)-4,8-dipiperidino-pyrimido[5,4-d]pyrimidin, which has the generic name dipyridamole, and its preparation have been described in U.S. Pat. No. 3,031,450.
Dipyridamole is a well known vasodilator and also has platelet aggregation inhibiting properties. In view of these properties, it has found widespread use for many years in the treatment of chronic coronary insufficiency and in the prophylaxis and treatment of heart infarcts as well as in the prophylaxis of arterial thrombosis.
More recently, the possible use of dipyridamole in tumor therapy has been investigated. This interest has derived from the observation that while it does not damage DNA, dipyridamole is an effective blocker of the salvage pathway of DNA synthesis, and that it can inhibit nucleoside transport through the cell membrane and so block restoration of internal cellular nucleoside levels, thus potentially inhibiting important steps in tumor cell synthesis. Biochem. Biophys. Acta, 58:435-447, (1968), and Biochem. Biophys. Acta. 211:88-94, (1970).
In view of this property, the effects of dipyridamole, both alone and in combination with various anti-cancer agents, have been investigated. Thus, Chan et al., Cancer Treat. Rep., 69:425-430, (1985) found that dipyridamole can potentiate the activity of N- phosphoracetyl-L-aspartate (PALA) in vitro and in vivo. PALA is a pyrimidine anti-metabolite which is thought to inhibit an early step in de novo pyrimidine synthesis, causing depletion of intracellular pyrimidine nucleotides. In another study Chan et al., Cancer Research, 45:3598-3604 (1985) reported that dipyridamole increased PALA activity against a human ovarian carcinoma cell line while exhibiting no cytotoxicity of its own.
Zhen et al., Cancer Research, 43:1616-1619, (1983), reported that the addition of a combination of cytidine, deoxycytidine and guanosine at an optimal concentration of 8 .mu.M each protected rat hepatoma 3924 A cells from the growth-inhibitory action of the antiglutamine drug Acivin, and that this protection was blocked by dipyridamole at a concentration of 6 .mu.M.
Nelson et al., Cancer Research 44: 2493-2496, (1984) reported that dipyridamole enhanced the toxicity of methotrexate (MTX) towards chinese hamster ovary cells both in vitro and in vivo: however, the antitumor activity of MTX towards certain other tumors, namely ridgway osteogenic sarcoma and LIZIO leukemia was not dramatically improved.
Various other publications describe the testing of dipyridamole together with anti-cancer agents against tumor cells, e.g. with cytarabine (Cancer Treat. Rep. 68: 361-366, (1984) and 2'-deoxyadenosine (Cancer Research 45: 6418-6424, (1985)
In addition, some investigations have been carried out on the use of dipyridamole alone as an anti-cancer drug. Thus, in the investigation on the combined action of dipyridamole/acivin, Weber, Cancer Research 73: 3466-3492, (1983), also showed that dipyridamole was effective in killing Hepatoma 3924A cells. Bastida, Cancer Research 45: 4048-4052, (1985), reported a potential metastatic effect of dipyridamole, possibly resulting from inhibition of tumor cell metabolism or suppression of one or more of the mechanisms involved in the ability of tumor cells to activate platelets.
Work has also been carried out on the structurally related compound 2,6-bis-(diethanolamino)-4-piperidino-pyrimido[5,4-d]pyrimidine (Mopidamole) as an anti-cancer drug.
Gastpar, Laryng, Rhinol., Otol, 62: 578-525 (1983) reported that mopidamole potentiates the antimitotic effect of interferon and its natural killer cell activating activity. He reports in the same article that " the adding of mopidamole to a culture of a human promyelocytic leukemic cell line promotes a reverse transformation of malignant cells to normal which appears to be a permanent phenotypic change. Furthermore, mopidamole was shown to diminish significantly spontaneous lung metastases in syngeneic Wilms Tumor (nephroblastoma) of the rat, the C1300 neuroblastoma of the mouse and the HMKim mammary carcinoma of the rat."
The use of mopidamole in the above investigation was based on its ability to increase cAMP levels, resulting in an inhibition of .sub. 3Hthymidine incorporation into neoplastic cells and a direct inhibition of the mitotic rate. The effect on cAMP levels derives from mopidamole's inhibition of PDE induced decomposition of cAMP, it may also stimulate the synthase and/or release of prostacyclin from the vessel wall which in turn activates adenylate cyclase involved in cAMP synthesis. Dipyridamole is, however, known to be much weaker PDE inhibitor than mopidamole.
It must also be observed that the teaching in the literature of the combination of mopidamole with interferon is confusing. Ambrus, J.L. et al. Proc. Am. Assoc. Cancer Res. 23: 183 (1932) state that mopidamole potentiates the antitumor effect of leukocyte and fibroblastic interferon in tissue culture, and in Proc. Soc. Exp. Biol. Med. 177: 487-490 (1984) state that mopidamole potentiates the growth inhibitory effect of human fibroblastic .beta.-interferon. Wolf et al., J. MED. 15-21 (1984) concludes that, in contrast to its effect with human fibroblast interferon, no synergistic inhibitory effect between mopidamole and a variety of .alpha.and .gamma.interferon could be observed. Finally, Ambrus et al. Proc. Am. Assoc. Cancer Res. 24: 309 (1983) state that, in contrast to some previous reports, no synergism was seen between interferon and mopidamole.
Galabov et al. Acta. Virol. 26 (3): 137-174 (1982) described a investigation with dipyridamole. European Patent Application 0.084.953. Galabov et al, reported that dipyridamole induced interferon production in vitro in explanted mouse peritoneal leukocytes and other cells and it induced interferon in mice after I.V. administration. However, this work has not been confirmed by other groups.
It is no where taught or suggested in the literature either to use dipyridamole in combination with an interferon in antitumor therapy, or suggested that any worthwhile results could be expected from such a combined therapy.